1. Field of the Invention
The present invention relates generally to non-contact condensation detecting methods and non-contact condensation detecting apparatuses, and more particularly to a non-contact condensation detecting method and a non-contact condensation detecting apparatus to easily detect dew condensation.
2. Description of the Related Art
Conventionally, there are methods of measuring the flow velocity and the flow rate of a fluid, and components and density of an atmosphere by detecting heat transported by the fluid and heat propagating in the atmosphere. A sensor serving as a detecting unit in a thermal flowmeter is configured as follows. A heater serving as a heat generation source is arranged on an upstream side of a flow of gas, and a temperature sensor is arranged on a downstream side of the flow of gas. The sensor measures the flow velocity and the flow rate based on the heat quantity (amount of temperature change) conveyed to the downstream side or the time it takes for the heat to reach the downstream side. Further, a sensor serving as a detecting unit in a hygrometer or a gaschromatograph measures humidity or components and density of gas based on heat quantity (amount of temperature change) propagated, or the time it takes for heat to be transported from a heater serving as a heat generation source in an atmosphere. The heat conductivity changes according to components or the density of the atmosphere. In the sensor serving as the detecting unit, the heat quantity of the heater serving as the heat generation source and the temperature sensor can be reduced, and the heater and the temperature sensor can be arranged extremely close to each other. With such a configuration, it is possible to accelerate thermal response, and detect rapid changes, a slight flow velocity/flow rate, minute amounts of components, or a minute level of density. The sensor is realized by microfabrication technology used for constructing integrated circuits. These types of sensors are conventionally called a flowsensor, a flow velocity sensor, a heat conductivity humidity sensor, or a heat conductivity gas sensor.
A flowsensor disclosed in Patent Document 1 includes a substrate having a through hole or a void, and a membrane heater section and a membrane detecting section bridged or cantilevered above the through hole or the void. The heater sections and the detecting sections are formed by laminating two or more layers along the flow direction of fluid to be measured, and interlayer spaces are provided. The spaces are formed by the thickness of layers, and are therefore formed highly accurately at minute intervals. Accordingly, the space distance between the membrane heater section and the membrane detecting section can be reduced so as to achieve fast responses, high precision, low fluid rates, and high efficiency.
A flowsensor disclosed in Patent Document 2 is realized by making a heater wire circular, making an isothermal line of a temperature distribution by the heat of the heater wire concentric, and also making temperature sensor wires at both sides of the heater wire concentric. Accordingly, whichever direction a fluid comes from, an isothermal line for each direction expands in the same shape with respect to the heater wire and the temperature sensor wire. Thus, detected values and detection sensitivity are not dependent on the direction of the fluid, so that the flow velocity or the flow rate can be detected regardless of the direction of the fluid. Specifically, a heater and a temperature sensor are arranged adjacent to each other on a plane. Gas is heated according to heat and the flow rate generated by the heater arranged at an upstream side. The heat quantity transported by the gas is captured (sensed) by the temperature sensor arranged at a downstream side, and is detected as a rise in the temperature. Moreover, the temperature sensor wire is shaped in accordance with the shape of the isothermal line of a temperature distribution of the heat from the heater wire. According to the configuration described in Patent Document 2, the temperature sensor wire is shaped in accordance with the shape of the isothermal line of a temperature distribution of the heat generated by the heater wire, and therefore, slight shifts of the isothermal line caused by slight changes in the flow rate or the flow velocity can be detected in substantially the entire area of the temperature sensor line. Thus, a highly sensitive flowsensor can be provided.
According to the Patent Documents 1, 2, it is understood that heat diffused in a three-dimensional space can be captured by making the temperature sensor three-dimensional, so as to surround the heater. Moreover, because it is necessary to detect the flow where influence from the surface of the substrate is minimal, the temperature sensor is to be arranged at a position distant from the substrate. The temperature sensor is to have a three-dimensional structure.
Patent Document 3 proposes a technology for fabricating three-dimensional components. According to the Patent Document 3, for low pressures of plasma gas, film stress in sputter-deposited coatings is compressive. As the pressure of the plasma gas increases, the film stress in a deposited sub-layer changes to a tensile stress. The intrinsic stress of many sputtered thin films depends on the ambient pressure at which the material is deposited. By varying the pressure during sputtering, films can be obtained that are compressively stressed near the substrate-film interface and tensile stressed at the film surface. A bottom gold layer forms the outer skin of a coil when released, and a release layer is removed by wet undercut etching. A possible etchant for a Si release layer includes KOH (wet processing). After removing a release window, each elastic member coils back on itself, due to an intrinsic stress profile of the elastic member. The foregoing techniques can also be used to manufacture a new type of high-Q variable capacitor (varicap). These varicaps use the same micro-spring technology described above, have the requisite capacitance values, and can be integrated on-chip. A varicap structure based on micro-springs allows both otherwise missing on-chip RF passive components, inductors and varicaps, to be fabricated using the same process technology. These micro-spring varicaps have the additional benefit of requiring lower bias voltages than parallel plate MEMS capacitors. By using a spring as the second electrode in a photolithographically patterned capacitor, and varying the voltage between a fixed plate and the spring, the capacitance of the structure varies.
Patent Document 1: Japanese Patent No. 3,049,122
Patent Document 2: Japanese Laid-Open Patent Application No. H11-118553
Patent Document 3: Japanese Publication of International Application No. 2003-533897
However, the following difficulties are faced according to Patent Document 1. Specifically, the heat from the heater at the upstream side diffuses three-dimensionally toward the downstream side, but the flow does not diffuse three-dimensionally because the flow path narrows. Therefore, the heat is easily transported to the temperature sensor. However, as the flow path is a solid object having higher heat conductivity than that of the fluid, excessive heat is conducted to the inner walls of the flow path due to the narrowed shape. As a result, the temperature sensor receives heat conduction components from the flow path, and a precise measurement cannot be performed. Moreover, because the heat quantity is large, heat accumulates in the substrate, and heat transferred from the substrate is added to the flow. This also affects the measurement of the temperature sensor located downstream. Further, as the units are arranged close to each other with high positional accuracy, adverse affects may be minimal. However, the positional relationship between the heater, the temperature sensor, and the substrate needs to be considered. Specifically, the distance between the heater and the temperature sensor is to be shorter than the distance between the heater and the substrate, and the heater and the temperature sensor need to be as far away from the substrate as much as possible.
According to Patent Document 2, the sensor is supposed to measure the flow in the middle of the flow; however, the sensor actually detects the flow at the surface of the substrate. More specifically, the sensor needs to detect the flow at a position least affected by the substrate surface. As the flow comes closer to the substrate surface, it flows less smoothly due to frictional resistance in the substrate surface. Thus, as the distance between the substrate becomes shorter, interference from the substrate increases. Accordingly, a slight flow rate cannot be measured. In addition, it is difficult to measure fluid of high viscosity, and at a temperature where the viscosity increases. In this configuration, the heater and the temperature sensor are arranged adjacent to each other on the plane. Gas is heated according to heat and the flow rate of the heat generated by the heater arranged at an upstream side. The heat quantity transported by the gas is captured by the temperature sensor arranged at a downstream side, and is detected as a rise in temperature. Moreover, the temperature sensor wire is shaped in accordance with the shape of the isothermal line of a temperature distribution of the heat of the heater wire. However, the heater and the temperature sensor are arranged adjacent to each other on the same plane, and the heat from the heater at the upstream side diffuses three-dimensionally toward the downstream side, and therefore, the temperature sensor can only capture a single plane component of the diffused heat components. As a result, the conveyance efficiency of heat and sensitivity is low, such that a low-noise, high resolution signal processing circuit is required. Also, in order to address the impact of a turbulence element, the temperature sensor needs to capture the three-dimensional isothermal line of three-dimensional heat diffusion.
Patent Document 3 discloses a three-dimensional coil formed on a chip. However, this structure is used as a contact point in variable capacitors and magnet coils, and is not intended for a heater and temperature sensor in a heat transportation mechanism. Due to the difference in functions, materials, shapes, and arrangements are different from those of a heat transportation mechanism. Thus, new configurations need to be added to realize a heater and temperature sensor in a heat transportation mechanism. To realize a sensor in a heat transportation mechanism for measuring the flow velocity or the flow rate of a fluid in a pipe and a space, the distance between the heater and the temperature sensor needs to be shorter than the distance between the heater and the substrate, and the heater and the temperature sensor need to be as far away from the substrate as possible. The temperature sensor needs to capture the three-dimensional isothermal line of three-dimensional heat diffusion as much as possible.
Conventionally, dew condensation has been a problem in various devices. Specifically, elements made of materials having high specific heat, and devices of large mass cannot adjust to rapid changes in the temperature/humidity in the surrounding environment. Therefore, dew condensation occurs on the surface, which causes malfunction of the device. Examples of such elements include optical recording media such as VTR head cylinders, hard disks, and optical disks; optical equipment such as lenses, light emitting devices, mirror reflectors, prisms, filters; optical devices including these optical equipment items; and components of image forming apparatuses such as photoconductive drums, polygon mirrors, and windows of automobiles and aircrafts. Dew condensation on the surfaces of these elements significantly affects functions of devices.
Moisture and gas adhering on recording sheets in electrophotographic image forming apparatuses significantly affect the image quality. Thus, it is required to accurately detect how the behavior of moisture adhering on the material surface is associated with the atmosphere, and control the behavior in an optimal manner. When a recording sheet dries as moisture in the sheet evaporates due to environmental changes, or when a recording sheet dries as moisture in the sheet undergoes rapid transpiration by receiving heat from a fixing unit, the recording sheet may deform by shrinking, curling, or creasing. Deformation needs to be prevented, because conveyance failures may occur while the sheet is being conveyed. In the fields of plants/animals and medicine, it is also necessary to detect water absorption phenomena or transpiration phenomena on surfaces of biologic objects, to examine the association with metabolism of biologic objects.
Japanese Laid-Open Patent Application No. 2002-310876 discloses a porous waterproof moisture permeable film that is porous on one side, allowing water vapor to permeate, but waterproof on the other side. If dew condensation water is formed on the porous side, the pores are blocked, and permeability to water vapor deteriorates. Accordingly, it is necessary to detect dew condensation.
Japanese Laid-Open Patent Application No. 2002-369885 discloses a power generating unit in which an electrocatalytic layer and a solid electrolyte membrane are combined. Gas transportation is less pronounced when dew condensation water is adhering, in a liquid state, on the solid electrolyte membrane. Gas transportation is more pronounced in a highly water-retentive state immediately before the condensation, and reaction efficiency of hydrogen and air is enhanced. Accordingly, it is necessary to detect the water retention rate of the solid electrolyte membrane.
In a cooling system, etc., disclosed in WO00/14522, in order to control cooling and dehumidifying operations in an optimal manner, it is necessary to detect the dew condensation on the surface of frozen materials near the surface of a heat exchanger in the cooling system side.
In a method of separating an organic solvent by distillation disclosed in Japanese Laid-Open Patent Application No. 2004-083385, the temperatures of aggregation and transpiration can be more precisely controlled by directly observing the gas behavior in the atmosphere, rather than detecting the temperature of the heat exchanger.
As described above, it is required in various fields to detect hydrophilia/hydrophoby on surfaces by quickly detecting aggregation and transpiration behaviors with high sensitivity, and detecting the differences in absorption of gas vapor molecules onto various surfaces.
There are conventional technologies for detecting dew condensation. Patent Document 4 discloses a condensation detection device. A VTR rotatable cylinder device has large heat capacity and dew condensation is thus likely to occur. Due to dew condensation, magnetic tape may adhere to the rotatable cylinder and get tangled. To prevent this problem, the condensation detection device determines whether the atmosphere is shifting into a supersaturation state. Specifically, the condensation detection device measures the surface temperature of the rotatable cylinder and the temperature and the humidity of the atmosphere near the rotatable cylinder, and then refers to data of the moisture amount in the air (psychrometric diagram), to make the determination.
Patent Document 5 discloses a method for measuring dew point or gas concentration, and an ice accretion predicting device. Dew condensation is detected based on a dew point obtained from the relative humidity of the atmosphere and the temperature of the subject of measurement. This method employs a relative humidity sensor employing a dielectric polymer, which responds more quickly to dew condensation than a mirror cooling method. An electrostatic capacity type, quick-response relative humidity sensor employing a dielectric polymer is cooled externally when the relative humidity is low. When the temperature is near the dew point, where the relative humidity rises, the relative humidity sensor is under a highly humid environment and is likely to maintain moisture, which makes it difficult to predict ice accretion. Thus, the relative humidity sensor is heated externally so as to change the temperature of the relative humidity sensor, thereby enhancing measurement precision.
Patent Document 6 discloses a dew condensation predicting device. Dew condensation is predicted by thermally binding a thermoelectric element to a dew condensation sensor to lower the temperature of the dew condensation sensor lower than the atmospheric temperature. In performing this operation, if water droplets are retained on the dew condensation sensor for a long time, the material of the sensor deteriorates. Thus, the dew condensation sensor is heated with the thermoelectric element to remove the dew condensation water from the dew condensation sensor.
Patent Document 7 discloses a sensor for predicting change of phase and a device for preventing frosting and dewing. Specifically, a dew condensation sensor is mounted onto a detection subject through a Peltier element. Heat is prevented from being transferred to/from the detection subject, so that the temperature of the dew condensation sensor is constantly lower by a fixed value than the surface of the detection subject. Dew condensation thus occurs faster on the dew condensation sensor than on the detection subject, so that frosting and dewing can be predicted.
Patent Document 8 discloses a temperature sensor for vehicles. The casing of a sensor for detecting the temperatures in various areas in a vehicle and the windshield of the vehicle are connected by a cup-shaped heat bonding member made of a heat conductive material. Incident infrared rays from the various areas are detected by a sensor element. When the temperature distributions at the various areas enter a predetermined range, the sensor determines that dew condensation has occurred on the windshield.
Patent Document 9 discloses a non-contact temperature measuring apparatus that utilizes the fact that heat flow between a reference object and an external object is proportional to the temperature of the external object. The non-contact temperature measuring apparatus detects, using a temperature sensor, temperatures of a first reference object and a second reference object that are spaced apart from each other by a certain distance along a moving continuous body. Accordingly, the temperature of the moving body is calculated.
Patent Document 10 discloses a technology for preventing a conveyance failure of a recording sheet in an electrophotographic image forming apparatus, caused by curling or creasing of the recording sheet while being conveyed. Specifically, an infrared ray moisture meter is used to detect the amount of moisture included in various parts of a recording sheet. According to the detected amount of moisture, the amount of air to be blown against various parts of the recording sheet is adjusted. This prevents the recording sheet from curling partially due to uneven amounts of moisture. In a technology disclosed in Patent Document 11, the amount of moisture included in a recording sheet is detected based on variations in transmission of a certain wavelength of infrared light reflected from the recording sheet. Based on the detected amount of moisture, the fixing temperature of a fixing device and roller pressure in a paper conveying path are controlled. In a technology disclosed in Patent Document 12, moisture included in a recording sheet is detected by using a moisture meter equipped for measuring the absorption of microwaves. The extent to which the recording sheet will curl is predicted based on the detected moisture amount and the type of the recording sheet, i.e. the strength (body) of the recording sheet. According to the prediction, curling of the recording sheet is corrected.
Patent Document 4: Japanese Laid-Open Patent Application No. H3-78648
Patent Document 5: Japanese Patent No. 2801156
Patent Document 6: Japanese Laid-Open Patent Application No. H1-127942
Patent Document 7: Japanese Laid-Open Patent Application No. H4-128643
Patent Document 8: Japanese Laid-Open Patent Application No. 2004-66927
Patent Document 9: Japanese Patent No. 3292523
Patent Document 10: Japanese Laid-Open Patent Application No. 2005-170525
Patent Document 11: Japanese Laid-Open Patent Application No. 2001-301273
Patent Document 12: Japanese Patent No. 2902130
In the condensation detection device disclosed in Patent Document 4, the dew condensation sensor needs to be attached to the rotatable cylinder of the VTR rotatable cylinder, in accordance with dew condensation properties of the rotating cylinder. If the dew condensation sensor is attached like a generic sensor, it cannot detect dew condensation. Moreover, there are restrictions in attaching the dew condensation sensor to the rotatable cylinder, because of functions of a magnetic head and electrical signals received by the rotatable member.
According to the method of dew condensation detection disclosed in Patent Document 5, or the devices disclosed in Patent Documents 6, 7, the sensor is heated externally, or the sensor is cooled to a temperature lower than the atmosphere. Accordingly, the temperature of the atmosphere measured by the sensor is different from that of the atmosphere of the subject of dew condensation. As a result, precision of detection deteriorates, because the sensor detects a different temperature from that of the atmosphere of the subject of condensation.
In the method of estimating dew condensation disclosed in Patent Document 8, the sensor needs to be mounted onto the surface that is the subject of dew condensation, and thus cannot be used generically. The non-contact temperature measuring apparatus disclosed in Patent Document 9 is capable of measuring the temperature of a remote object in a non-contact manner by measuring the temperature gradient of gas; however, gas-liquid phase changes cannot be measured by this method.
Each of the dew condensation sensors described above detects whether dew condensation has occurred on itself. However, these dew condensation sensors cannot detect whether dew condensation has occurred on the actual subject.
The dew condensation sensors described above require special means in thermal structures to accommodate properties of dew condensation on the subject. Therefore, the dew condensation sensors cannot detect dew condensation of the subject by simply being attached to the subject, or being disposed near the subject.
The dew condensation sensors described above have dew condensation prediction functions. However, each of these sensors operates as a system using a dew condensation prediction algorithm obtained by adding a detected temperature of a specific location in the device. Accordingly, these sensors can only be applied to specific devices, and cannot be used universally.
By using an optical means such as a mirror cooling type dew point meter to measure dew condensation of a subject object from a remote location, only a mirror surface can be measured. Accordingly, this type of means cannot be generically used to measure any type of surface. A conceivable method is to detect a dew condensation phenomenon by combining a humidity sensor with an infrared thermometer. However, the emissivity differs according to surface conditions, and therefore, an accurate temperature cannot be measured. The temperature can be measured only for the portions of the surface where emissivity is known, and it is not certain whether the humidity of the surface of the subject object is detected.
In an image forming apparatus, deformation of a recording sheet, such as curling, is caused when the recording sheet dries rapidly. Specifically, the direct cause of the deformation is the speed of drying. The drying speed of a recording sheet depends on the speed at which moisture in the recording sheet is reduced by transpiration. The transpiration behavior reflects the quality and structure of the recording sheet, and the strength of the recording sheet determined by the quality and structure thereof. Thus, as described in Patent Documents 10, 12, it is difficult to predict deformation such as curling of a recording sheet with high precision, even by detecting the amount of moisture included in the recording sheet.